Not sure if you're referring to telegram or signal. If you're referring to signal:
Is it private? Can I trust it? - Signal Support
Signal conversations are always end-to-end encrypted, which means that they can only be read or heard by your intended recipients. Privacy isn’t an optional mode — it’s just the way that Signal works. Every message, every call, every time.
The complete source code for the Signal clients and the Signal server is available on GitHub. This enables interested parties to examine the code for security and correctness.
To be fair "potential next president" already answers if someone is corruptable